In the prior art methods of synthesis of physiologically active compounds, 10-{.beta.-[N/1,4-diazabicyclo-(4,3,0)-nonanyl/propionyl]}-2-chlorophenoth iazine dichlorohydride and .gamma.-[N-/1,4-diazabicyclo-(4,3,0)-nonanyl/]-propyl-parafluorophenyl ketone dichlorohydride use is made of octahydropyrrolo-[1,2-a]-pyrazine which, in turn, is prepared by reducing hexahydropyrrolo-[1,2-a]-pyrazin-1-one with lithium alumohydride in the medium of diethyl ether. The starting hexahydropyrrolo-[1,2-a]-pyrazin-1-one is prepared by a multistage synthesis from .delta.-chlorovaleric acid (cf. Likhoscherstov et al., J. Org. Chem. (USSR), volume VI, p. 1729 (1970) involving bromination of .delta.-chlorovaleric acid in the presence of PCl.sub.3, esterification of the resulting product, followed by a condensation thereof with ethylenediamine. This method has the disadvantage of the necessity of using a hazardous and rarely-available lithium alumohydride, a hazardous solvent and the difficulty of preparation of the starting hexahydropyrrolo-[1,2-a]-pyrazin-1-one.
Also known in the art is a method of preparing octahydropyrrolo-[1,2-a]-pyrazine by the catalytic dehydration a furandiamine. This prior art method has the disadvantage of complicated technology with respect to the process of dehydration of N-tetrahydrofurfurylethylenediamine in a quartz tube at a temperature within the range of from 300.degree. to 315.degree. C. over alumina activated with zirconia. This method is difficult to implement commercially on a large scale. Another disadvantage of the method is the low yield of the desired product, i.e. about 30%.